In the pharmaceutical field several lung diseases, like bronchial asthma, are treated with powdered drugs to be delivered, by means of dispensing inhalation devices, in very accurate doses to be frequently repeated.
A dispensing device for these drugs should guarantee an accurate and reproducible dosage, a perfect nebulization, which means the reduction of the powder to "respirable particles" having a diameter of less than 7 microns, avoiding or disintegrating eventual powder lumps, and the powderized drug isolation from the outside environment, to ensure its stability and preservation.
These three characteristics, dosage accuracy, fineness of nebulization and drug stability have, up to now, been obtained all together only with the use of aerosol metered dispensers provided with a container in which the powderized drug is dispersed into pressurized FREON.
But the aerosol system and its relative FREON or CFC propellent shall not be further allowed in the near future and furthermore the use of propeleny in general requires to add to the drug tensioactive or lubricant additives which have shown negative side effects when inhaled.
A way of administering powderizod drug able to avoid the use of CFC propellent and additives is represented by the powder inhaler devices.
The main characteristic of these devices is that the delivery of the drug is obtained by the air flow generated at inhalation which, passing through a dosage chamber containing the powderized drug, forms the particle cloud which is then inhaled, thus avoiding the need of propellent.
In these systems, as the powderized drug, particles often tend to lump together forming too large particles to be inhaled, the user has to provide an inhalation flow whose force is enough high to first move the particles and then disintegrate them during their run through the inhaler conduits.
This breathing force cannot be achieved by many asthmatic patient and therefore only very low dosage devices and drugs have demonstrated to be enough widely usable in most of the situations.
The document WO-A-9 204 068 discloses an inhalator without propellant gas comprising a triggerable pump which can be manually precharged before starting inhalation and can be triggered in synchronism with the respiration. Disadvantageously, this device is very complicated and may therefore lead to failures and problems during the operation and the assembly process. Furthermore, in operation, the dosage chamber is moved from the reservoir in an air channel, whereby some of the content of the dosage chamber can be lost before the air stream blows through the air channel. The dosage accuracy is therefore not guaranteed.
To overcome this problem, some inhalers use packs capsules each containing a single dose of the powderized drug, and more recently systems incorporating a multidose powder reservoir have been introduced on the market.
One of the most recent version of this system incorporates one or more dosage chambers, obtained as holes in a rotable element associated to the drug reservoir, holes which are filled by dosage means contained into the drug reservoir.
These means consist in elastic spring loaded scrapers arranged to press against the perforated element surface.
These scrapers, due to their flexed position at an angle lower than 90.degree. degrees against the perforated element and thanks to the thrust given by the spring loading and by their resilient characteristics, do exert a pressure on the micronized powder and compress it into, the dosage holes when they slide under them.
Nevertheless this compression of the powderized drug could create, in certain cases, some inconvenient which could compromise the dose accuracy.
In fact the micronized powders, when compressed, tend to stick together and to form lumps of various and relatively large dimension, and scrapers in general, keep under compression at least the quantity of drug which is retained between themselves and the rigid surface against which they urge.
These agglomerates are not always removed or disintegrated by the scrapers and could therefore obstacle the correct filling of the dosage holes or chambers.
Further to that this compression could create "compactings" of different and not controllable density inside the dosage holes, thus creating possible variations in the delivered quantities.
The above is further particularly relevant in case of relatively large required doses (from 2 to 10 mg and over) as in the use of Sodium Cromoglycate or of mixtures of different drugs.
In these cases, in fact, larger and mainly deeper dosage holes are needed, which makes their filling much more difficult.
Furthermore the deeper holes reduce the effectiveness of a scraper as a filling device as, due to its shape, it cannot enter deep into the hole to be filled.